In the process of manufacturing active-matrix organic light emitting diode (AMOLED) display devices, mask plates are usually used for vapor deposition. Before the vapor deposition, it is needed to place one mask plate on a carrying platform of a lithography system. Before performing photolithography, it is needed to ensure that a mask mark of the mask plate is within CCD field of view. After the mask plate is aligned, the photolithography can be performed successively. In the above process, it is needed to hold or fix the mask plate within a region. However, in the related art, a position of the mask plate on the carting platform is stable, which easily causes color mixing on edges of display devices.